Silicon oxide-coated soft magnetic powder and method for producing same

Abstract

A silicon oxide-coated soft magnetic powder has excellent insulating property and provides a high powder compact density. In making the powder, silicon alkoxide is added to a slurry containing soft magnetic powder containing iron in an amount of 20% by mass or more dispersed in a mixed solvent of water and an organic solvent containing water in an amount of 1% by mass or more and 40% by mass or less. A hydrolysis catalyst for the silicon alkoxide is then added to perform silicon oxide coating. The coated magnetic powder has a coverage factor R of 70% or more defined by R=Si×100/(Si+M) (wherein Si and M represent molar fractions of Si and elements constituting the soft magnetic powder obtained by an XPS measurement), a powder compact density of 4.0 g/cm3 or more, and high μ′ at high frequency and high insulating property.

1 . Silicon oxide-coated soft magnetic powder comprising soft magnetic powder containing iron in an amount of 20% by mass or more, having coated on a surface thereof a silicon oxide, the silicon oxide coating layer having an average thickness of 1 nm or more and 30 nm or less, a coverage factor R defined by the following expression (1) of 70% or more, and a powder compact density of 4.0 g/cm 3  or more:
     R=Si× 100/( Si+M )  (1)
   
       wherein Si represents a molar fraction of Si obtained by an X-ray photoelectron spectroscopy (XPS) measurement of the silicon oxide-coated soft magnetic powder, and M represents a total of molar fractions of metal elements and non-metal elements except for oxygen among elements constituting the soft magnetic powder obtained by the XPS measurement. 
     
     
         2 . The silicon oxide-coated soft magnetic powder according to  claim 1 , wherein the silicon oxide-coated soft magnetic powder has a volume based cumulative 50% particle diameter D 50  obtained by a laser diffraction particle size distribution measurement method of 1.0 μm or more and 5.0 μm or less. 
     
     
         3 . A method for producing silicon oxide-coated soft magnetic powder containing soft magnetic powder containing iron in an amount of 20% by mass or more, having coated on a surface thereof a silicon oxide, the method comprising:
 a step of mixing water and an organic solvent to prepare a mixed solvent containing water in an amount of 1% by mass or more and 40% by mass or less;   a dispersing step of adding soft magnetic powder containing iron in an amount of 20% by mass or more to the mixed solvent to provide a slurry having dispersed therein the soft magnetic powder;   an alkoxide adding step of adding a silicon alkoxide to the slurry having dispersed therein the soft magnetic powder;   a hydrolysis catalyst adding step of adding a hydrolysis catalyst for the silicon alkoxide to the slurry having dispersed therein the magnetic powder having the silicon alkoxide added thereto, so as to provide a slurry having dispersed therein soft magnetic powder coated with a silicon compound;   a step of subjecting the slurry having dispersed therein soft magnetic powder coated with a silicon compound to solid-liquid separation, so as to provide soft magnetic powder coated with the silicon oxide; and   a step of drying the soft magnetic powder coated with the silicon oxide.   
     
     
         4 . The method for producing silicon oxide-coated soft magnetic powder according to  claim 3 , wherein the silicon oxide coating layer of the silicon oxide-coated soft magnetic powder has an average thickness of 1 nm or more and 30 nm or less, a coverage factor R defined by the following expression (1) of 70% or more, and a powder compact density of 4.0 g/cm 3  or more:
     R=Si× 100/( Si+M )  (1)
   
       wherein Si represents a molar fraction of Si obtained by an X-ray photoelectron spectroscopy (XPS) measurement of the silicon oxide-coated soft magnetic powder, and M represents a total of molar fractions of metal elements and non-metal elements except for oxygen among elements constituting the soft magnetic powder obtained by the XPS measurement. 
     
     
         5 . The method for producing silicon oxide-coated soft magnetic powder according to  claim 3 , wherein the silicon oxide-coated soft magnetic powder has a volume based cumulative 50% particle diameter D 50  obtained by a laser diffraction particle size distribution measurement method of 1.0 μm or more and 5.0 μm or less.